Effects of desensitization of capsaicin-sensitive afferent neurons on gastric microcirculation in rats depend on the blood glucocorticoid hormone level

The effects of desensitization of capsaicin-sensitive afferent neurons on gastric microcirculation were investigated before and after administration of indomethacin at ulcerogenic dose in adrenalectomized rats with or without corticosterone replacement and in sham-operated animals. We estimated the blood flow velocity in submucosal microvessels; the diameters and permeability of mucosal venous microvessels as parameters of gastric microcirculation. Desensitization of capsaicin-sensitive neurons was performed with capsaicin at the dose 100 mg/kg two weeks before the experiment. Adrenalectomy was created one week before experiment. In vivo microscopy technique for the direct visualization of gastric microcirculation and the analysis of the blood flow was employed. Indomethacin at ulcerogenic dose decreased the blood flow velocity in submucosal microvessels, caused dilatation of superficial mucosal microvessels and increased their permeability. Desensitization of capsaicin-sensitive afferent neurons potentiated indomethacin-induced microvascular disturbances in gastric submucosa-mucosa. These potentiated effects of the desensitization are obviously promoted by concomitant glucocorticoid deficiency. Thus, glucocorticoid hormones have a beneficial effect on gastric microcirculation in rats with desensitization of capsaicin-sensitive afferent neurons.     

Aggravation of nonsteroidal antiinflammatory drug gastropathy by glucocorticoid deficiency or blockade of glucocorticoid receptors in rats

Our previous investigations suggest that the reduction of stress-induced corticosterone release, or inhibition of corticosterone actions, promotes stress-induced gastric erosions in rats. In this study the effect of glucocorticoid deficiency on susceptibility to gastric mucosal injury by nonsteroidal antiinflammatory drugs (NSAIDs) was evaluated in rats. Gastric erosions induced in male rats by indomethacin (25 mg/kg sc) or acidified aspirin (40 mM po) were studied one week after adrenalectomy with or without corticosterone replacement or after occupation of glucocorticoid receptors by the antagonist RU-38486 during the period of erosion formation. Corticosterone for replacement (4 mg/kg sc) was injected 15 min before the administration of indomethacin or acidified aspirin to adrenalectomized rats. The antagonist RU-38486 (10 mg/kg po) was administered twice, 20 min before and 60 min after NSAID administration. Plasma corticosterone levels were measured by fluorometry. Gastric erosions were quantitated by measuring the area of damage. Indomethacin or acidified aspirin induced both plasma corticosterone rise and gastric erosions. Adrenalectomy decreased both basal and NSAID-induced corticosterone levels and markedly promoted gastric erosion formation caused by the NSAID. An acute corticosterone replacement mimicking indomethacin-and aspirin-induced corticosterone rise prevented the effect of adrenalectomy on the gastric erosions. The administration of the glucocorticoid/progesterone antagonist RU-38486 significantly potentiated the formation of gastric erosions induced by indomethacin as well as aspirin. These observations suggest a gastroprotective action of glucocorticoids released in response to NSAID treatment against NSAID-induced injury.     

Gastroprotective action of glucocorticoids during the formation and the healing of indomethacin-induced gastric erosions in rats.

The aim of the present study consisted of the investigation of glucocorticoid role in the formation and the healing of indomethacin-induced (25 mg/kg, s.c.) gastric erosions in rats. The effect of deficiency of glucocorticoid production followed by corticosterone replacement on the formation and the healing of the gastric erosions was evaluated. Glucocorticoid production was decreased by adrenalectomy or by delayed inhibitory action after a single pharmacological dose of cortisol (300 mg/kg i.p.) injected 1 week before the onset of ulcerogenic stimulus. Indomethacin induced corticosterone rise and caused gastric erosions. The loss of indomethacin-induced plasma corticosterone rise potentiated the formation of indomethacin-induced erosions in both models. The area of gastric erosions in rats with glucocorticoid deficiency was considerably larger than that in control animals 4 h after indomethacin administration as well as during 48 h after the drug administration (period of erosion healing). Injecting corticosterone in rats with glucocorticoid deficiency significantly decreased the formation of indomethacin-induced gastric erosions and promoted their healing. Thus, the present data support the gastroprotective action of glucocorticoids in the formation and in the healing of indomethacin-induced mucosal injury.     

Transformation of physiological gastroprotective effects of glucocorticoids into pathological ulcerogenic consequences

The study was designed to investigate how physiological gastroprotective action of glucocorticoids could be transformed to pathological proulcerogenic effect. Time-dependent effects of single injection of dexamethasone on stress-induced gastric erosions, corticosterone and blood glucose levels, somatic parameters were investigated in fasted rats. Dexamethasone injected at the same dose attenuated or aggravated the stress-induced gastric erosions depending on the time of the injection. In case of dexamethasone injection 1-12 hrs before stress, we observed its gastroprotective action. Further increase in the time interval caused transformation of the gastroprotective action of dexamethasone to proulcerogenic effect. Accordingly to the results obtained, dexamethasone-induced long-lasting maintenance of blood glucose levels accompanied with signs of catabolic effect as well as dexamethasone-induced corticosterone deficiency may be responsible, at least partly, for the transformation of gastroprotective effect of dexamethasone to the proulcerogenic one.     

Anti-inflammatory effects of angiotensin II AT1 receptor antagonism prevent stress-induced gastric injury

Stress reduces gastric blood flow and produces acute gastric mucosal lesions. We studied the role of angiotensin II in gastric blood flow and gastric ulceration during stress. Spontaneously hypertensive rats were pretreated for 14 days with the AT1 receptor antagonist candesartan before cold-restraint stress. AT1 receptors were localized in the endothelium of arteries in the gastric mucosa and in all gastric layers. AT1 blockade increased gastric blood flow by 40-50%, prevented gastric ulcer formation by 70-80% after cold-restraint stress, reduced the increase in adrenomedullary epinephrine and tyrosine hydroxylase mRNA without preventing the stress-induced increase in adrenal corticosterone, decreased the stress-induced expression of TNF-alpha and that of the adhesion protein ICAM-1 in arterial endothelium, decreased the neutrophil infiltration in the gastric mucosa, and decreased the gastric content of PGE2. AT1 receptor blockers prevent stress-induced ulcerations by a combination of gastric blood flow protection, decreased sympathoadrenal activation, and anti-inflammatory effects (with reduction in TNF-alpha and ICAM-1 expression leading to reduced neutrophil infiltration) while maintaining the protective glucocorticoid effects and PGE2 release. Angiotensin II has a crucial role, through stimulation of AT1 receptors, in the production and progression of stress-induced gastric injury, and AT1 receptor antagonists could be of therapeutic benefit.     

The effects of desensitization of capsaicin-sensitive neurons on the blood flow in microvessels of the rat gastric serous muscular membrane with normal and insufficient contents of glucocorticoids

The effects of desensitization of capsaicin-sensitive neurons on the blood flow velocity in microvessels of the gastric muscular membrane were investigated before and after indomethacin (35 mg/kg) administration in adrenalectomized rats with or without corticosterone replacement (4 mg/kg sc) and in sham-operated animals. Desensitization of capsaicin-sensitive neurons was performed with neurotoxic dose of capsaicin (20 + 30 + 50 mg/kg sc) two weeks before the experiment. Adrenalectomy was created one week before the experiment. The in vivo microscopy technique for direct visualization of gastric microcirculation and analysis of red blood cell (RBC) velocity was employed. Indomethacin decreased the RBC velocity. Adrenalectomy by itself profoundly decreased the RBC velocity, whereas corticosterone replacement prevented this effect. Desensitization of capsaicin-sensitive neurons did not influence the RBC velocity in sham-adrenalectomized rats; however, it induced further fall of both basal and indomethacin-induced RBC velocity in adrenalectomized rats that was prevented by corticosterone. We conclude that glucocorticoid hormones have a beneficial effect on the blood flow velocity in microvessels of the gastric muscular membrane in rats with desensitization of capsaicin-sensitive neurons.     

The role of glucocorticoids in healing of indomethacin-induced lesions in the rat gastric mucosa

Pretreatment with a single large dose of cortisol a week before indomethacin administration, or an adrenalectomy induced a glucocorticoid production deficiency in rats. The area of gastric erosions in these rats was considerably larger than in the control animals in 4, 24, and 48 hours after the indomethacin administration. Administration of corticosterone noticeably prompted the healing of the erosions in the rats with glucocorticoid deficiency. The findings suggest a gastroprotective effect of glucocorticoids in healing of indomethacin-induced mucosal injury.     

Deficiency of glucocorticoid production delays the healing of acute gastric mucosal erosion and chronic ulcers in rats

Effects of glucocorticoid deficiency followed by corticosterone replacement on the healing of gastric erosions and chronic gastric ulcers have been investigated in rats. Glucocorticoid deficiency was induced by adrenalectomy performed after the formation of gastric erosions or ulcers. Gastric erosions were produced by indomethacin (35 mg/kg, i.p.) or by 6 h immobilization at temperature 8 degrees C, chronic gastric ulcers were induced by 60% acetic acid. All ulcerogenic stimuli caused an increase in corticosterone production. Adrenalectomy created corticosterone deficiency and delayed the healing of gastric erosions and chronic gastric ulcers. The effect of adrenalectomy was more evident in the indomethacin ulcerogenic model. Replacement by corticosterone prompted the healing of gastric erosions and ulcers in adrenalectomized animals. These data suggest a participation of endogenous glucocorticoids in a restoration of gastric mucosal integrity.     

The role of endogenous glucocorticoids in maintenance of the gastric mucosa integrity

Effect of glucocorticoid deficiency on susceptibility to gastric mucosal injury by non-steroid anti-inflammatory drugs (NSAID) was studied in rats. The corticosterone production was inhibited by a single large dose of cortisol as well as by an adrenalectomy. The drop in the corticosterone production prompted gastric erosions induced by the NSAID. Replacing corticosterone prevented the effects of cortisol pretreatment of adrenalectomy on NSAID-induced gastric erosions. The data obtained reveal a gastroprotective effect of endogenous glucocorticoids.     

Current concepts in gastric microcirculatory pathophysiology.

When the barrier to acid back-diffusion is disrupted, there is a protective increase in gastric mucosal blood flow to help remove the back-diffusing acid. Only recently has the mechanism for calling forth this protective hyperemia been determined. The gastric mucosa and submucosa are innervated by many capsaicin-sensitive sensory nerve fibers containing vasodilator peptides. The gastric mucosal sensory neurons monitor for acid back-diffusion, and, when this process occurs, signal for a protective increase in blood flow via release of calcitonin gene-related peptide from the submucosal periarteriolar fibers. The endothelium-derived vasodilator, nitric oxide, plays an important role both in the maintenance of basal gastric mucosal blood flow and in the increase in blood flow that accompanies pentagastrin-stimulated gastric acid secretion. It also interacts with the capsaicin-sensitive sensory nerves in the modulation of the microcirculation to maintain mucosal integrity. Finally, it has been shown that neutrophils play an important role in various forms of mucosal injury. The leukocytes adhere to the vascular endothelium and contribute to injury by reducing blood flow via occlusion of microvessels, as well as by releasing mediators of tissue damage.     

Activation of hypothalamic-pituitary-adrenocortical system as important gastroprotective component of stress reaction

The review is focused on the action of glucocorticoids released during activation of hypothalamic-pituitary-adrenocortical axis, on the susceptibility of gastric mucosa to injury. The data support the idea that glucocorticoids produced in response to acute stress or other ulcerogenic stimuli have a gastroprotective action but not ulcerogenic one as it has generally been considered for some decades. It has been shown that gastroprotective action of glucocorticoids may be mediated by multiple actions, including maintenance of glucose homeostasis, gastric mucosal blood flow, mucus production and attenuation of enhanced gastric motility and microvascular permeability. For maintenance of gastric mucosal integrity glucocorticoids may cooperate with other gastroprotective factors. Glucocorticoid hormones exert a pivotal role in the maintenance of gastric mucosal integrity in the case of impaired gastroprotective mechanisms provided by prostaglandins, nitric oxide and capsaicin-sensitive sensory neurons. These findings indicate that activation of hypothalamic-pituitary-adrenocortical system could be considered as a significant hormonal gastroprotective component of stress reaction and therefore glucocorticoid hormones are natural gastroprotective factors.     

Deficit of glucocorticoid production in rats aggravates ulcerogenic effects of stimuli of various modality and intensity

Effects of glucocorticoid deficiency and corticosterone replacement on gastric mucosal injury induced by various ulcerogenic stimuli have been evaluated in rats. Gastric erosions were induced in male rats by stimuli of different modalities and intensities. Glucocorticoid deficiency was induced by adrenalectomy or delayed inhibitory action after a single pharmacological dose of cortisol (300 mg/kg, i.p.) injected one week before the onset of ulcerogenic stimulus. Ulcerogenic stimuli induced both a plasma corticosterone rise and a gastric mucosal injury. The area of mucosal damages induced various stimuli ranging from a small to extensive those. Glucocorticoid deficiency significantly potentiated an ulcerogenic action of each ulcerogenic stimulus. Replacement by corticosterone (4 mg/kg, s.c., 15 min before the onset of ulcerogenic stimulus) prevented or significantly decreased the erosion--potentiating effect of glucocorticoid deficiency. These results show that endogenous glucocorticoids released during ulcerogenic influences help gastric mucous membrane to resist against a harmful action of both weak and strong ulcerogenic stimuli.     

Endogenous opiates and stress ulceration

Parenteral administration of the opiate antagonist, naltrexone, had a cytoprotective effect against stress-induced ulceration. This effect appears to be due to blockade of peripheral rather than central endogenous opiates and is not related to the central inhibitory effect of opiates on gastric acid secretion. Opiates have complex effects on gastric mucosal blood flow which may explain their role in stress ulceration.     

Effects of stress on immune responsiveness, gastric ulcerogenesis and plasma corticosterone in rats: modulation by diazepam and naltrexone

Effects of restraint stress (24 hr at room temperature) were evaluated on some immunological, visceral and endocrinal responses in rats. In animals sensitized with sheep RBC (SRBC), restraint stress (a) prevented the booster-induced rise in anti-SRBC antibody titre, (b) induced gastric mucosal erosions, and (c) elevated plasma corticosterone, when compared to non-stressed controls. Diazepam (1 or 10 mg/kg) consistently attenuated the effects of stress on all three parameters studied. The opioid antagonist, naltrexone (1 or 5 mg/kg) tended to aggravate these stress-induced effects. These concurrent biological changes during stress and their modulation by drugs are discussed in light of a possible correlation between endocrinal, immunological and visceral changes during such aversive stimuli.     

Various ulcerogenic stimuli are potentiated by glucocorticoid deficiency in rats

The effects of glucocorticoid deficiency with or without corticosterone replacement on susceptibility to gastric mucosal injury by various ulcerogenic stimuli have been evaluated in rats. Gastric erosions were induced in male rats by stimuli of different modalities and intensities: 20% ethanol (po), aspirin (300 mg/kg, ip), acidified aspirin (40 mM, po) and 100% acetic acid (applied to gastric serosa). Glucocorticoid supply was decreased by adrenalectomy or by delayed inhibitory action after a single pharmacological dose of cortisol (300 mg/kg, ip) injected one week before the onset of ulcerogenic stimulus. Corticosterone for replacement (4 mg/kg, sc) was injected in rats with glucocorticoid deficiency 15 min before the onset of ulcerogenic stimulus. Plasma corticosterone levels were measured by fluorometry. Gastric erosions were quantitated by measuring the area of damage. Ulcerogenic stimuli induced both plasma corticosterone rise and gastric mucosal injury. The area of mucosal damages induced various stimuli ranged from small to extensive. Glucocorticoid deficiency significantly potentiated an ulcerogenic action of every ulcerogenic stimulus. Replacing corticosterone prevented or significantly decreased erosion-potentiating effect of glucocorticoid deficiency. These results show that endogenous glucocorticoids released during ulcerogenic influences help gastric mucosa to resist a harmful action of both weak and strong ulcerogenic stimuli.     

Transforming growth factor alpha-mediated gastroprotection against stress ulceration in the rat: involvement of capsaicin-sensitive sensory neurons

Exogenously administered TGF alpha has been shown to protect rodent gastric mucosa against injury caused by acid-dependent and acid-independent injury. The present study examined whether the gastroprotective effects of TGF alpha on stress-induced gastric ulceration in the rat involves activation of capsaicin-sensitive sensory neurons. Fasted male SD rats were subjected to water restraint stress (WRS) for four hours. Thereafter, rats were euthanized; the stomach opened and macroscopic areas of gastric ulceration quantitated (mm(2)). Gastric tissue contents of TGF alpha and the sensory neuropeptide, calcitonin gene-related peptide (CGRP) were determined by radioimmunoassay. Prior to stress rats received TGF alpha 50, 100 or 200 microg/kg by intraperitoneal injection. Sensory denervation was accomplished by high dose capsaicin treatment. WRS caused severe ulceration in the gastric corpus; 46.1 + 6.6 mm(2). Parenteral administration of TGF alpha caused dose-dependent reduction in gastric injury: 34.7 + 4.9 mm(2) with 50 microg/kg (p < 0.05); 25.4 + 3.6 mm(2) with 100 microg/kg (p < 0.001) and 9.4 + 0.8 mm(2) with 200 microg/kg (p < 0.001). The gastroprotective action of TGF alpha (200 microg/kg, i.p.) was abolished by capsaicin-induced sensory denervation. In addition, WRS ulceration was associated with significant reduction in gastric CGRP (-42%) and TGF alpha (-48%) content. Reduction in CGRP content was prevented by TGF alpha pretreatment. We conclude that: 1) TGF alpha caused dose-dependent gastroprotection against WRS ulceration, 2) TGF alpha-mediated gastric mucosal protection was prevented by capsaicin-induced sensory denervation and, 3) stress-induced injury was associated with significant reduction in gastric content of both TGF alpha and CGRP.     

Homeostasis in the gastric mucosa and blood circulation. Part 1. Mechanisms of the adequate blood flow maintenance in the gastric mucosa]

The increase of mucosal blood flow in response to food entrance into stomach or different irritant action is the component of gastric mucosal defence barrier. Sufficient blood flow ensures normal acid-bicarbonate balance in gastric mucosa, supports the healing process and prevents superficial damages from developing into deep ones. Capsaicin-sensitive afferent nerve fibers play the large role in the blood flow regulation. The influence of these nerve fibers on the gastric blood flow is mediated by the calcitonin-gene related peptide. This peptide released from peripheral afferent terminals improves microcirculation in stomach walls. Moreover nerve impulses from afferent neurons modulate parasympathetic activity that in turn induces the increase of gastric mucosal blood flow through both choilinergic and noncholinergic mechanisms. The gastric mucosal blood flow may be also regulated by humoral and paracrine metabolites. Nitric oxide and prostaglandines are the most important low molecular weight compounds. They play the main role in the maintenance of the basal gastric mucosal blood flow and in the development of hyperemic responses to harmful agents.     

Blood flow regulation in the cerebral microvasculature with an arcadal network: a numerical simulation

Blood flow regulation in the cerebral microvasculature with an arcadal network was investigated using a numerical simulation. A mathematical model for blood flow in the arcadal network, based on in vivo data of cat cerebral microvasculature and flow velocity was developed. The network model consists of 45 vessel segments and 25 branching points. To simulate microvascular response to blood flow, non-reactive (solid), cerebral arteriole-like, or skeletal muscle arteriole-like responses to wall shear stress were taken into account. Numerical calculation was carried out in the flow condition where the inlet (arterial) pressure was changed from 60 to 120 mmHg. Flow-rate in each efferent vessel and the mean flow-rate over all efferent vessels were evaluated for assessment of blood supply to the local area of cerebral tissue. The simulation demonstrated the wall shear stress-induced vasodilation in the arcadal network worked to maintain the blood flow at a constant level with pressure variable in a wide range. It is suggested that an individual microvessel (segment) should join in the regulatory process of flow, interacting with other microvessels (cooperative regulation).     

Effects of serotonin and stress on the state of the gastric mucosa in rats with the intact and transsected vagus nerve

In experiments on vagotomized and intact rats with the use of two models of experimental gastric ulceration (injection of serotonin and stress) it was demonstrated that the inhibitory action of vagotomy on haemorrhagic gastric effectiveness was more pronounced in stress than after serotonin application. Vagotomy decreased stress-induced erosive lesions but increased serotonin-induced erosions that may be a result of the increase of gastric tissue sensitivity to this amine which developed simultaneously with significant decrease of its level in gastric wall after vagotomy. Serotonin-antagonist peritol decreased stress-induced gastric disturbances in vagotomized rats more significantly than in intact rats; this suggested the great role of serotonin in anti-ulcerogenic effect of vagotomy.     

Disorders of Autonomic Control of Microcirculation in Explosion-Induced Coal-Mine Trauma: Experimental Modeling,Pathogenetic Analysis,and Pharmacological Correction

We modeled the consequences of explosion-induced coal-mine trauma, ECMT, i.e., contusion, intoxication by explosion products, burns, emotional stress, etc., in rats using a specially developed device. ECMT was produced by a dosed explosion of a methane-air mixture. In addition, the device allowed us to model effects of coal-mine occupational factors, CMOF (high air pressure, temperature, and humidity, high contents of dust and alien gases in the air, and intensive physical loading). We examined modifications of microcirculation in the vessels of the abdominal cavity (mesenterial vessels) after ECMT and after such a trauma aggravated by the premorbid action of CMOF (for 1 h daily over 14 days). The long-lasting influence of CMOF evoked noticeable vasoconstriction and a drop in the volume velocity of blood flow through the mesenteric vessels. Both complicated and noncomplicated ECMT resulted in significant dilatation of the mesenteric vessels (their mean diameter increased in 1 h by about 40% as compared with the norm) and an increase in the volume blood flow velocity (by 71 and 41% as compared with the norm, respectively). Injections of 3 mg/kg diazepam (i.p., immediately after ECMT) considerably corrected the shifts of the pressure in and linear velocity of blood flow through the microvessels under study, whereas their diameter and the volume flow velocity remained increased (the former, somewhat, and the latter, significantly). The mechanisms of disorders of regional circulation evoked by the actions of ECMT and CMOF in the visceral microvessels (with special attention to metabolic factors, which evoke vasodilation), the importance of the phenomenon of blood sequestration in these vessels to the clinical course of ECMT, and approaches for pharmacological correction of the above disorders by drugs of the benzodiazepine family are discussed.